Method for preparing polyorganosiloxanes (pos) by polycondensation/redistribution of oligosiloxanes in the presence of a strong base and strong bases used

ABSTRACT

The invention concerns the synthesis of silicone by anionic polymerisation of cyclic organosiloxane oligomers in the presence of a slightly nucleophilic strong base. The invention aims at providing novel strong base catalysts, more efficient in terms of solubility in the silicones, with hydrolysis stability strength and polymerising capacity. To achieve this, the invention provides for the use of ylides derived from aminophosphonium such as for example that of formula: [Me3N)3P—CHMe2]+, MeO or derived from phosphoranylidenes such as that of formula: [Me3P—HC=Pme3]+, t-BuO. The invention also concerns strong base catalysts as novel products.

The field of the invention is that of the synthesis of the silicones:PolyOrganoSiloxanes (POSs), by anionic polymerization(polycondensation/redistribution) of linear or cyclic, preferablycyclic, OligoOrganoSiloxanes (OOSs).

More specifically, the invention relates to a process for thepreparation of POSs by polycondensation/redistribution of cyclicOligoOrganoSiloxanes (OOSS) in the presence of a catalyst (or initiator)composed of a strong base (superbase) which is weakly nucleophilic, thatis to say non-nucleophilic toward centers other than protons.

The invention is also targeted at catalysts of superbase type employedin these reactions for the polycondensation/redistribution of cyclicOligoOrganoSiloxanes (OOSs) resulting in POS oils (molar mass ranging,for example, from 10³ to 10⁴) or in POS gums (molar mass ranging, forexample, from 10³ to 10⁷).

These superbases belong to the family of the aminophosphonium ylides orto the family of the carbodiphosphorane derivatives.

The invention also relates to some of these superbases as novel productsper se.

Silicones are nowadays widely used in industry. Most of them arepolymerized siloxanes or are based on these derivatives. For thisreason, the synthesis of these polymers by polycondensation ofbifunctionalized silanes or by opening of oligosiloxane rings is a veryimportant line of research and numerous publications on this subjecthave appeared. Polymerization by ring opening of oligosiloxanes usesmonomers which can be readily synthesized and purified and, in addition,it makes possible better control of the molecular weight of the polymerobtained. It is consequently the method of choice generally employed forsynthesis of high molecular weight polymers. In practice, this method isto date the only industrial route.

Polymerization by the opening of oligosiloxane rings is a complexprocess:

The monomers currently used are generally octamethylcyclotetrasiloxane(D₄) and hexamethylcyclotrisiloxane (D₃). Polymerization can be carriedout by the anionic or cationic route.

The cationic route is often preferred for the synthesis of linear POSsas the reaction takes place at a sufficiently fast rate at ambienttemperature and the initiator can be easily removed from the polymer.The drawback to this method is the significant formation of cyclic OOSs,which appear particularly at the beginning of the polymerization. Thismethod of polymerization is based on the increase in the reactivity ofthe Si—O bond for monomers having a strained ring, such ascyclotrisiloxanes. The use of these substrates makes it possible tooperate under conditions of kinetic control.

On the other hand, the anionic route is generally used for the formationof linear polymers of high molecular weight. This process comprises 3stages:

-   -   1) the initiation phase is the attack on the siloxane by the        base to result in the formation of a silanolate at the chain        end:    -   2) extension/shortening of the chains:    -   3) interchain exchanges (mixing of chains, redistribution):        M corresponds to an alkali metal in the above schemes.

Under these conditions, there is no stage of halting polymerization.When the equilibrium conditions are reached, the yield of polymer, itsmolecular weight and its weight distribution are entirely controlled bythe thermodynamics of the polymerization. These parameters arecompletely independent of the initiator used. This method ofpolymerization makes possible the synthesis of high molecular weightpolysiloxanes with a narrow distribution. This is because, in this case,the depolymerization and the interchain exchanges are slower than thepropagation reaction.

Many different initiators are used to carry out this polymerization, forexample alkali metal or alkaline earth metal hydroxides or complexes ofalkali metal or alkaline earth metal hydroxides with alcohols, andalkali metal or alkaline earth metal silanolates. The reaction can becarried out under dry conditions, in a solvent or in an emulsion. Thepolymerization can be halted by using an acid additive which reacts withthe initiator or the polymer chains to render the latter unreactive.Furthermore, these additives can be used to regulate the molecularweight of the polymer and/or to add an advantageous property. In themajority of cases, the residues from the initiator remain in the polymerproduced or are removed, for example by filtration. This is highlydisadvantageous to the industrial process for thepolycondensation/redistribution of cyclic OOSs in the presence of K⁺OH⁻or SiO⁻M⁺, which process additionally has the major disadvantage ofbeing lengthy (for example, 15 hours) at high temperature (e.g.,150-180° C.).

Phosphonium salts are known as other basic catalysts which can beenvisaged. Thus, the use of phosphonium hydroxides as initiator wasdescribed for the first time at the end of the 1950s (Gilbert, A. R. andKantor, S. W., J. Polym. Sci., 1959, 40, 38-58). Tetramethyl- andtetraethylphosphonium hydroxides polymerize D₄ at 110° C. but thecatalyst has a short lifetime which prevents the formation of longpolymers. It is the same for the other known types of phosphoniumhydroxides. This instability is totally unacceptable in the context ofthe application targeted by the present invention.

A renewal of interest in phosphorus derivatives became clear whenphosphazenes, for example the compound of formula:

These phosphazenes are extremely strong non-nucleophilic bases(pK_(a)=42) and have been described as superbasic catalysts for thepreparation of POSs from cyclic OOSs. They are thus described in thefollowing European patent applications EP-A-0 860 459, EP-A-0 860 460and EP-A-0 860 461, which relate to the use of phosphazene superbases offluoride type of 1 for the polymerization by opening of OOS rings in thepresence of water and optionally of a filler (silica), indeed even whileblocking the polymerization reaction using CO₂ or acid.

Patent US-B-5 994 490 discloses a similar system is obtained by mixingthe phosphazenes:

(pK_(a)≈32) and a tertiary alcohol: e.g. tert-butanol. Polymerizationtakes place at a relatively high temperature of 100° C., which can be ahandicap at the industrial level.

The following European patent applications EP-A-1 008 598, EP-A-1 008610, EP-A-1 008 611 and EP-A-1 008 612 themselves also disclosephosphazene superbases of [(Me₂N)₃P═N—((Me₂)N₂P═N)_(n)P⁺(NMe₂)] OH⁻ or[(Me₂N)₃P═N]₃P═N-t-Bu type in the polymerization by opening of OOSrings.

French patent application FR-A-2 708 586 discloses linear phosphazenesof formulae: OCl₂P(NPCl₂)_(n)NPCl₂X with X═OH, O. or Cl, of use ascatalysts in the polycondensation and the redistribution of POSs, andthe reaction products of these linear phosphazenes with water or analcohol.

In a completely different field, WO-A-98/54229 discloses the use ofphosphorus ylides of formula (Me)₂C═P(NMe₂)₃ [and of their precursors(Me)₂C—P⁺(NMe₂)₃ Y⁻ with Y=halogen or triflate] as weakly nucleophilicstrong base in reactions for the C-alkylation of lactams, succinimides,oligopeptides and benzodiazepines.

In such a state of the art, one of the essential objects of the presentinvention is to provide a process for the preparation ofPolyOrganoSiloxanes (POSs) by polycondensation/redistribution ofoligosiloxanes using effective novel basic catalysts which are:

-   -   soluble in silicone oils and in particular silicone gums;    -   simple and inexpensive to synthesize;    -   stable;    -   endowed with good stability toward hydrolysis; and which make it        possible:    -   to polymerize OOSs, such as D₄, under mild conditions (low        temperatures ≦100° C.);    -   to reduce the reaction times, in particular in the preparation        of viscous oils and of gums;    -   to reduce, indeed even to eliminate, catalyst residues and        residues of its derivatives in the final polymer, in order to        prepare silicone polymers of high viscosity and with improved        thermal stability, and in a profitable way;    -   to functionalize a whole pallet of cyclic or linear and        functionalized or non-functionalized siloxane monomers;    -   to improve the polydispersity of polymers formed and to favor        the formation of linear structures in comparison with cyclic        oligomers;    -   to easily remove possible catalyst residues;    -   to favor the formation of linear silicone polymers in comparison        with the formation of cyclic silicone polymers;    -   to guarantee high reproducibility;    -   and to limit sensitivity to the variability in the starting        materials.

Another essential object of the present invention is to provide novelcatalysts composed of strong superbases, with a pK_(a) of between 10 and40, which are not very nucleophilic, so as to limit side reactions, inthe preparation of PolyOrganoSiloxanes (POSs) bypolycondensation/redistribution of oligosiloxanes, it being necessaryfor said catalysts to meet the above specifications.

Another essential object of the present invention is to provide novelstrong superbases, with a pK_(a) of between 10 and 40, which are notvery nucleophilic.

These objects, among others, are achieved by the present invention,which relates first of all to a process for the preparation ofPolyOrganoSiloxanes (POSs) by polycondensation/redistribution ofoligosiloxanes in the presence of a catalyst comprising at least onestrong base, characterized in that this strong base is chosen from thegroup consisting of:

-   -   aminophosphonium ylide derivatives of following formula (I):    -   in which:        -   the R¹ symbols, which are identical to or different from one            another, each represent an alkyl, an aryl, an aralkyl or an            alkylaryl;        -   the R² symbols, which are identical to or different from one            another, each represent a hydrogen, an alkyl, an aryl, an            aralkyl or an alkylaryl;        -   R corresponds to hydrogen or to an alkyl, an aryl, an            aralkyl or an alkylaryl;    -   phosphoranylidene derivatives of following formulae (II),        (II^(x)), (II′) and (II^(x′)):    -   in which:        -   the R⁴ symbols, which are identical to or different from one            another, each represent an alkyl, an aryl, an aralkyl or an            alkylaryl;        -   the R⁵ symbols, which are identical to or different from one            another, each represent a radical corresponding to the same            definition as that given above for R⁴;        -   R′ corresponds to hydrogen or an alkyl, an aryl, an aralkyl            or an alkylaryl;        -   x, y, z, m¹, m², x′, y′ and z′ are positive integers and            -   x=y×z            -   m¹×m²=2            -   x′=2×y′×z′.

According to a preferred embodiment of the process according to theinvention, the catalytic system defined above is an alkoxide.

It has been shown, in accordance with the invention, that the catalystsof formula (I) and the catalysts of formulae (II), (II^(x)), (II′) and(II^(x′)) correspond to the abovementioned requirements and areeffective in the polymerization of OOSs, such as D₄ in the presence ofM₂: R₃Si—O—SiR₃. These catalytic systems are novel and operate at 25° C.Equilibrium is, for example, achieved after approximately 1 hour (levelof linear polymer ˜87%) whereas current industrial conditions require areaction time, for example, of 6-8 h at 160° C. using catalysis by apotassium silanolate. These phosphonium and phosphoranylidene alkoxidesare stable.

Mention may be made, as example of catalyst (I), of that resulting fromthe reaction between a precursor (Ip1.1) and methanol according to therelationship (where Me═CH₃):

Mention may be made, as another example of catalyst (I), of thatresulting from the reaction between:

-   -   a precursor of phosphonium halide type (Ip2.1) where        i-Pr=isopropyl:    -   and potassium tert-butoxide (t-BuOK),    -   to give the catalyst:        and the salt KI.

By virtue of the invention, POSs can be obtained with yields of morethan 60-70% in the presence of the catalysts or initiators as definedabove.

In accordance with the invention, the OR⁻ and OR′⁻ anions of theformulae (I), (II), (II^(x)), (II′) and (II^(x′)) can originate from thereaction between an alcohol or water and an ylide precursor or abis(triphenylphosphoranylidene)methane and they are preferably chosenfrom those with a pK_(a) of between 10 and 30 and which are not verynucleophilic.

Preferably, the R or R′ radical is chosen from hydrogen and alkyls,preferably from C₁-C₆ alkyls and more preferably still from the groupconsisting of methyl, isopropyl, n-propyl, n-butyl and t-butyl.

It is apparent, in the context of the invention, that the alcoholsretained in the superbasic catalytic systems can be classified bydecreasing effectiveness in the following order:

-   -   tertiary alcohol (for example t-butanol, where        R═R′=t-butyl) >secondary alcohol (for example isopropanol where        R═R′=isopropyl) >primary alcohol (for example methanol where        R═R′═CH₃).

One of the surprising advantages of the carefully selected superbases inaccordance with the invention is due to the possibility of rapidreaction at low temperature. Thus, the process is characterized in thatthe polycondensation/redistribution is carried out at a temperature T (°C.) such that: T ≦ 100 preferably 15 ≦ T ≦ 70 and more preferably still15 ≦ T ≦ 60.

In practice, the temperature is ambient temperature, which isparticularly economical and easy to employ industrially.

Quantitatively, the concentration of catalyst C (ppm with respect to thestarting oligosiloxanes) in the reaction medium is such that: C ≦ 10000preferably  500 ≦ C ≦ 7000 and more preferably still 2000 ≦ C ≦ 5000.

In fact, the rate of polymerization is slightly dependent on the amountof initiator.

According to an advantageous arrangement of the invention, thepolycondensation/redistribution is halted by heating the reactionmedium, preferably to a temperature between 100 and 150° C., and/or byaddition of water to the reaction medium.

To facilitate the purification of the POS polymer formed, it can beenvisaged, in accordance with the invention, to attach the catalysts(I), (II), (II^(x)), (II′) and (II^(x′)) according to the invention to apolymer support, for example to a resin.

As regards the superbasic catalyst of formula (I), the R¹ substituentsof the nitrogen are chosen from alkyls, preferably from C₁-C₆ alkyls andmore preferably still from the group consisting of methyl, isopropyl,n-propyl, n-butyl and t-butyl; methyl being very especially preferred;with respect to the R² substituents of the carbon, they correspond tothe same definition as that given above for R¹ and, in addition, theycan represent a hydrogen atom.

According to a first preferred embodiment of the process of theinvention, a catalyst (I) is used and at least one solution of at leastone precursor (Ip1) of the catalyst (I) is used, the formula (Ip1) beingas follows:

in which the R¹ and R² radicals correspond to the same definition asthat given above, it not being possible for R² to represent a hydrogen,in at least one solvent of formula ROH, with R as defined above.

The optimization of the system involves the use of an amount of solventROH such that the latter is in excess with respect to the compound(s)(Ip1). Advantageously, this amount is from 2 to 5 equivalents of ROH perone equivalent of compound(s) (Ip1).

Methodologically, it appeared desirable to use the solvent of thecompound(s) (Ip1) which has been used for its synthesis, so that thesolution of (I) in ROH comprises at least one other solvent (Ip1). Thismakes it possible to improve the yields and the rate of polymerization.By way of example, it may be specified that the system “compound (Ip1)(0.5 mol %)/t-BuOH (5 equiv.)” is particularly advantageous in thepolymerization of D₄ (e.g.: M_(w)=16 700, Yd=87%). In addition, atambient temperature, the degree of conversion of D₄ can be 50% after 30minutes and 84% after 1 hour, with a molar mass of the order of 27 000,for example.

It should be noted that, in this first embodiment, it is possible touse, in the polycondensation/redistribution reaction medium: (i) eitherthe compound of formula (I) taken in isolation after separation from itsmedium for preparation by reaction of the precursor (Ip1) with analcohol or water; (2i) or, preferably, the crude reaction solution asobtained on conclusion of the reaction of the precursor (Ip1) with analcohol or water.

According to a second preferred embodiment of the process of theinvention, recourse is had to the catalyst (I) and the introduction iscarried out, into the OOSs polycondensation/redistribution reactionmedium, of the purified or unpurified product of the reaction, describedas counteranion exchange, between:

-   -   a compound of phosphonium halide type (Ip2) which is the        precursor of the catalyst (I), the formula of (Ip2) being as        follows:        in which the R¹ and R² symbols correspond to the same definition        as that given above, it being possible for R² in addition to        represent a hydrogen, and X corresponds to a chlorine, bromine        or iodine atom,    -   and an alkali metal alkoxide ROM derived from an aliphatic        primary, secondary or tertiary monoalcohol ROH (R being other        than H) having from 1 to 6 carbon atoms and from an alkali metal        M, such as, for example, sodium or potassium, the counteranion        exchange reaction being carried out in a solvent medium        comprising at least one polar aprotic solvent chosen, for        example, from tetrahydrofuran, dimethyl sulfoxide, carbon        tetrachloride and hexamethylenephosphoramide.

The optimization of the counteranion exchange reaction involves the useof solutions of alkoxide ROM in the alcohol which has given rise to it,which solutions can include up to 20 mol of alcohol and which solutionspreferably include from 1 to 10 mol of alcohol per one mole of alkoxidebase. Use is in addition made of 2 to 6 mol and preferably of 3 to 5 molof alkoxide base ROM per one mole of compound (Ip2).

By way of example, it may be specified that the system “1 equivalent ofcompound (Ip2)/3 equivalents of alkoxide ROM/15 equivalents of alcoholROH/300-500 equivalents of THF” is particularly advantageous in thepolymerization of D₄.

The expression “purified or unpurified product” is understood to meanthat it is possible to employ, in the polycondensation/redistributionreaction medium: (i′) either the aminophosphonium alkoxide of formula(I) taken in isolation after separation from its preparation medium;(2i′) or the unfiltered crude reaction solution as obtained onconclusion of the counteranion exchange reaction; (3i′) or the crudereaction solution filtered in order to separate therefrom the MX saltformed. The forms (2i′) and (3i′) are preferred.

As regards the superbasic catalyst of formulae (II) and (II′), the R⁴substituents are chosen from linear or branched alkyls and/or aryls,preferably from C₆-C₈ aryls or C₁-C₆ alkyls and more preferably stillfrom the group consisting of phenyl, methyl, isopropyl, n-propyl,n-butyl and t-butyl; methyl being very especially preferred.

According to one alternative form, the R⁴ radicals can be substituted byheteroatoms, for example halogens.

When R⁴=phenyl, the cation of the formula (II) is, for example, thatresulting from bis(triphenylphosphoranylidene)methane and the alkoxideanion is that where R′ represents t-butyl or isopropyl (IPA):

When R⁴=methyl, the cation of the formula (II) is, for example, thatresulting from bis(trimethylphosphoranylidene)methane and the alkoxideanion is that where R′ represents t-butyl or isopropyl (IPA):

When the R⁴ symbols represent methyls and isopropyls, the catalyst offormula (II) is, for example, bis(diisopropylmethylphosphonium)methylenetert-butoxide of formula:

The superbases of formula (II′) can, for example, comprise cations:

According to the formula (II′), it is possible to have severalmonovalent anions or one monovalent anion bonded to one polyvalentcation or to several monovalent cations.

According to a third preferred form, recourse is had to the catalyst(II) and (II^(x)) and use is made, in the OOSspolycondensation/redistribution reaction medium, of at least onesolution of at least one precursor (IIp1):

in which the R⁴ symbols correspond to the same definition as that givenabove, in at least one solvent of formula R′OH, with R′ as definedabove.

The compounds (IIp1) result in the cations included in the catalysts offormula (II), which will form the entities (II) and (II^(x)), afterreaction with an alcohol (R′ is preferably alkyl and the alcohol is morepreferably t-butanol or isopropanol) or water (R′═H).

During this preparation in the reaction medium of the entities (II) from(IIp1), it is preferable for the solvent ROH to be in excess withrespect to the compound(s) (IIp1).

Advantageously, the solution of (IIp1) in ROH comprises at least oneother solvent S* of (IIp1). In this context, a solution of (IIp1) in S*is prepared and this solution is mixed with the solvent(s) ROH, thecompound(s) (IIp1) used to prepare this solution in S* being composed ofone (or more) evaporation residue(s).

It should be noted that, in this third embodiment, it is possible touse, in the polycondensation/redistribution reaction medium: (i) eitherthe compound of formula (II) taken in isolation after separation fromits medium for preparation by reaction of the precursor (IIp1) with analcohol or water; (2i) or, preferably, the crude reaction solution asobtained on conclusion of the reaction of the precursor (IIp1) with analcohol or water.

According to a fourth preferred embodiment of the process of theinvention, recourse is had to the catalyst (II) and the introduction iscarried out, into the OOS polycondensation/redistribution reactionmedium, of the purified or unpurified product of the reaction, describedas counteranion exchange, between:

-   -   a compound of phosphonium halide type (IIp2) which is a        precursor of the catalyst (II), the formula of (IIp2) being as        follows:        in which the R⁴ symbols correspond to the same definition as        that given above and X corresponds to a chlorine, bromine or        iodine atom,    -   and an alkali metal alkoxide R′OM derived from an aliphatic        primary, secondary or tertiary monoalcohol R′OH (R′ being other        than H) having from 1 to 6 carbon atoms and from an alkali metal        M, such as, for example, sodium or potassium, the counteranion        exchange reaction being carried out in a solvent medium        comprising at least one polar aprotic solvent chosen, for        example, from tetrahydrofuran, dimethyl sulfoxide, carbon        tetrachloride and hexamethylenephosphoramide.

The optimization of the counteranion exchange reaction involves the useof solutions of alkoxide R′OM in the alcohol which has given rise to it,which solutions can include up to 20 mol of alcohol and which solutionspreferably include from 1 to 10 mol of alcohol per one mole of alkoxidebase. Use is in addition made of 2 to 6 mol and preferably of 3 to 5 molof alkoxide base R′OM per one mole of compound (IIp2).

By way of example, it may be specified that the system “1 equivalent ofcompound (IIp2)/3 equivalents of alkoxide R′OM/15 equivalents of alcoholR′OH/60-200 equivalents of THF” is particularly advantageous in thepolymerization of D₄.

The expression “purified or unpurified product” is understood to meanthat it is possible to employ, in the polycondensation/redistributionreaction medium: (i′) either the alkoxide of formula (II) taken inisolation after separation from its preparation medium; (2i′) or theunfiltered crude reaction solution as obtained on conclusion of thecounteranion exchange reaction; (3i′) or the crude reaction solutionfiltered in order to separate therefrom the MX salt formed. The forms(2i′) and (3i′) are preferred.

In the polycondensation/redistribution process according to theinvention, the starting oligosiloxanes can be linear and can correspondto the following general formula:

-   -   in which:    -   R^(a) represents hydrogen or an alkyl or aryl radical,    -   and R^(b) corresponds to an alkyl or an aryl, optionally        comprising one or more heteroatoms and optionally substituted by        halogens, and p≧2.

However, preferably, the starting oligosiloxanes are cyclic andcorrespond to the following general formula:

-   -   in which:    -   R^(c) represents hydrogen or an optionally substituted alkyl,        alkenyl, aryl, aralkyl or alkylaryl radical,    -   and 3≦q≦12.

They are volatile cyclic cyclosiloxanes in which R^(a) is preferablychosen from alkyl groups having from 1 to 8 carbon atoms inclusive,optionally substituted by at least one halogen atom, advantageously fromthe methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups, and fromaryl groups and advantageously from the xylyl, tolyl and phenylradicals. Generally, at least 80% by number of these R^(a) radicals aremethyl radicals. In practice, they can be D₄ or D₃, optionally vinylatedand optionally as a mixture with M: (R^(b) ₃SiO_(1/2)).

The adjustment of the viscosity of the reaction medium during thepolymerization is within the scope of a person skilled in the art. Itcan be carried out by any means.

The reaction medium is subjected, except as regards the temperature,which is ambient temperature, to conventional reaction conditions.

Chain blockers can be employed. This can be polydimethylsiloxanesMD_(p)M with p=0 to 20, preferably 0 to 10.

Another subject-matter of the invention is the use, as catalyst in thepreparation of PolyOrganoSiloxanes (POSs) bypolycondensation/redistribution of oligosiloxanes, of compoundscomprising at least one strong base chosen from aminophosphonium ylidederivatives of following formula (I):

-   -   in which:    -   the R¹ symbols, which are identical to or different from one        another, each represent an alkyl, an aryl, an aralkyl or an        alkylaryl;    -   the R² symbols, which are identical to or different from one        another; each represent a hydrogen, an alkyl, an aryl, an        aralkyl or an alkylaryl;    -   R corresponds to hydrogen or to an alkyl, an aryl, an aralkyl or        an alkylaryl.

Another subject-matter of the invention is the use, as catalysts in thepreparation of PolyorganoSiloxanes (POSs) bypolycondensation/redistribution of oligosiloxanes, of compoundscomprising at least one strong base chosen from phosphoranylidenederivatives of following formulae (II), (II^(x)), (II′) and (II^(x′)):

-   -   in which:    -   the R ⁴symbols, which are identical to or different from one        another, each represent an alkyl, an aryl, an aralkyl or an        alkylaryl;    -   the R⁵ symbols, which are identical to or different from one        another, each represent a radical corresponding to the same        definition as that given above for R⁴;    -   R′ corresponds to hydrogen or an alkyl, an aryl, an aralkyl or        an alkylaryl;    -   x, y, z, m¹, m², x′, y′ and z′ are positive integers and        -   x=y×z        -   m¹×m²=2        -   x′=2×y′×z′.

The invention also relates, as novel products, to aminophosphonium ylidederivatives of following formula (I):

in which:

-   -   the R¹ symbols, which are identical to or different from one        another, each represent an alkyl, an aryl, an aralkyl or an        alkylaryl;    -   the R² symbols, which are identical to or different from one        another, each represent a hydrogen, an alkyl, an aryl, an        aralkyl or an alkylaryl;    -   R corresponds to hydrogen or to an alkyl, an aryl, an aralkyl or        an alkylaryl.

The invention also relates, as novel products, to phosphoranylidenederivatives of following formulae (II), (II^(x)), (II′) and (II^(x′)):

in which:

-   -   the R⁴ symbols, which are identical or different, each represent        an alkyl, an aryl, an aralkyl or an alkylaryl;    -   the R⁵ symbols, which are identical or different, each represent        a radical corresponding to the same definition as that given        above for R⁴;    -   R′ corresponds to hydrogen or an alkyl, an aryl, an aralkyl or        an alkylaryl;    -   x, y, z, m¹, m², x′, y′ and z′ are positive integers and        -   x=y×z        -   m¹×m²=2        -   x′=2×y′×z′.

Furthermore, the invention is targeted at the compounds of followingformulae (IIp1) and (IIp2) which can be used in particular as catalystprecursor in the preparation of PolyOrganoSiloxanes (POSs) bypolycondensation/redistribution of oligosiloxanes:

in which:

-   -   the R⁴ symbols, which are identical to or different from one        another, each represent an alkyl, an aryl, an aralkyl or an        alkylaryl;    -   X corresponds to a chlorine, bromine or iodine atom.

As regards the production of a catalyst according to the invention:

-   -   the precursors (Ip1) can be rapidly synthesized from commercial        compounds in two stages, for example according to the following        reaction scheme:    -   the precursors (IIp1) can be prepared, for example, by the        action of CCl₄ on the corresponding triaryl- and/or        trialkylphosphine:    -   the precursors (IIp2) can be prepared by combining, for example,        the following stages:        then the stage:        then the stage:        the final synthesis of the type (II) catalyst preferably taking        place in situ in the polymerization medium, for example        according to the reaction:

It is thus possible to readily access an entire series of superbases ofuse in the redistribution reactions of silicone oligomers.

EXAMPLES

NMR=Nuclear Magnetic Resonance

GPC=Gas Chromatography

Example 1 Superbase Ccatalyst Formed by theDimethyl-methylenetris(dimethylamino)phosphorane/Alcohol Mixture

A) Isopropyltris(dimethylamino)phosphonium Iodide (1)

18.7 g (110 mmol) of 2-iodopropane are added to 40 ml of diethoxymethanecomprising 5 ml (27 mmol) of HMPT in a two-necked flask equipped with areflux condenser. The mixture is left at reflux for 5 days. Thephosphonium salt precipitates as a white powder. The precipitate isfiltered off and washed with diethoxymethane (2×5 ml). The white productis dried under reduced pressure at ambient temperature for 10 h. Theyield is 65% (purity >98%). The ¹H and ³¹P NMR data of theisopropyltris(dimethylamino)phosphonium iodide are in agreement with thedata in the literature. The compound (1) may be purified byrecrystallization from acetonitrile.B) Dimethylmethylenetris(dimethylamino)phosphorane (2)

240 mg (6 mmol) of potassium hydride are added to a suspension of 1 g (3mmol) of salt (1) in 25 ml of THF in a Schlenk tube. The mixture ismaintained at ambient temperature for 12 h. The supernatant is recoveredby filtration with a hollow tube. The solvent is evaporated undervacuum. After two extractions with pentane (2×20 ml) under argon andevaporation of the latter under vacuum, the product (2) is obtained inthe form of a solid with an overall yield of 85%. The ¹H and ³¹P NMRdata of the product (2) are in agreement with the data in theliterature. The compound is stored in solution in pentane in arefrigerator.C) Polymerization of D₄ in the Presence of the Ylide (2) and ofTert-Butyl Alcohol

The in situ synthesis of the superbase catalyst (3) in thepolymerization medium from the ylide (2) and from tert-butyl alcohol canbe represented schematically as follows:

The solution of ylide (2) in pentane is placed in a Schlenk tube andevaporated under vacuum. 3-5 equiv. of t-BuOH are added. After 2 min,6.18 ml (0.02 mol) of D₄ and 111-222 ml (0.5-1 mmol) of M₂ are added.The mixture is maintained at ambient temperature. The reaction ismonitored by GPC.

The amounts of reactant and the results of the experiments are presentedin table 1. Under these conditions, the polymer was obtained with a goodyield in the presence of 1000 ppm of initiator and with a much loweryield if the amount of initiator is only 500 ppm. TABLE 1 Polymerizationof D₄ in the presence of the ylide (2) and of tert-butyl alcohol M₂Ylide t-BuOH Polym. (ppm/ (ppm/ (eq./ Time yield (%) M_(w) M_(z) Exp.D₄) D₄) ylide) (h) (GPC) (GPC) (M_(w)/M_(n)) 1 25000 5000 5 2 87 167001.3 2 50000 2500 3 2 88 16500 1.5 3 25000 1600 3 2 87 22600 1.3 4 250001000 5 2 85 22100 1.3 5 25000 500 5 20 10 37500 1.3

The kinetics of polymerization were studied. The results of theexperiments are presented in table 2. It is possible to obtain up to 87%of polymer in 1 h at ambient temperature. TABLE 2 Kinetics ofpolymerization of D₄ in the presence of the ylide (2)and of tert-butylalcohol Exp. M₂ Ylide t-BuOH Time Yd (%, No. (ppm/D₄) (ppm/D₄)(eq./ylide) (h) GPC) M_(w) 1 50000 2500 3 0.5 1 84 18400 3.5 87 15400 2088 16500 2 25000 1600 3 0.3 53 37700 1 87 27600 1.75 86 24200 2.5 8722300 16 87 21300 4 weeks 87 19100

The influence of the amount of tert-butanol on the polymerization wasstudied. The results of the experiments are presented in table 3. Thedecrease in the amount of alcohol makes it possible to accelerate therate of the reaction. TABLE 3 Influence of the amount of tert-butylalcohol on the polymerization of D₄ M₂ Ylide t-BuOH Polym. (ppm/ (ppm/(eq./ Time yield (%) M_(w) M_(z) Exp. D₄) D₄) ylide) (h) (GPC) (GPC)(M_(w)/M_(n)) 1 25000 5000 40 20 61 39700 1.3 2 25000 5000 5 2 87 167001.3

Preparation of MDpM (p=156)

A solution of 60.7 mg (0.296 mmol) of ylide (2) in pentane (4.5 ml) isplaced in a Schlenk tube and evaporated under vacuum. 85 μl (3 equiv.)of t-BuOH are added. After 2 min, 55.18 ml (0.178 mol) of D₄ and 0.99 ml(4.36 mmol) of M₂ are added. The mixture is maintained at ambienttemperature for 2 h. Volatile fractions are removed under vacuum at 100°C. for 12 h. A polymer with an M_(w) of 56 000 and with a polydispersityof 1.96 was obtained with a yield of 87%.

Preparation of MDpM (p=5000)

A solution of 78.6 mg (0.383 mmol) of the ylide (2) in pentane (5.5 ml)is placed in a Schlenk tube and evaporated under vacuum. 107 μl (3equiv.) of t-BuOH are added. After 2 min, 47.5 ml (0.153 mol) of D₄ and56 mg (0.122 mmol) of MD₄M are added. The mixture is maintained atambient temperature for 4 h. Volatile fractions are removed under vacuumat 100° C. for 12 h. A polymer with an M_(w) of 249 100 and with apolydispersity of 2.95 was obtained with a yield of 28%.

Preparation of MDpD^(vi)qM (p=3000, q=28)

A solution of 205 mg (0.383 mmol) of ylide (2) in pentane (10 ml) isplaced in a Schlenk tube and evaporated under vacuum. 286 μl (3 equiv.)of t-BuOH are added. After 2 min, 61.8 ml (0.2 mol) of D₄, 0.64 ml (1.85mmol) of D^(vi) ₄ and 0.12 mg (0.0265 mmol) of MD₄M are added. Themixture is maintained at ambient temperature for 4 h. Volatile fractionsare removed under vacuum at 100° C. for 12 h. A polymer was obtainedwith a yield of 82%.

Comparative test 1). Polymerization of D₄ in the presence of potassiumtert-butoxide

6.18 ml (0.02 mol) of D₄, 111 μl (5 mmol) of M₂ and 22.4 mg (0.2 mmol)of potassium tert-butoxide are placed in a Schlenk tube. The mixture ismaintained at ambient temperature for 20 h. The reaction is monitored byGPC. Polymerization does not occur. The mixture is subsequentlymaintained at 70° C. for 15 h. A polymer with an M_(w) of 28 700 andwith a polydispersity of 1.75 was obtained with an overall yield of 86%.

+Comparative test 2). Polymerization of D₄ in the presence of potassiumsilanolate

18.54 ml (0.06 mol) of D₄, 666 μl (30 mmol) of M₂ and 41.6 mg ofpotassium silanolate (14.4% KOH by weight; Rhodia sample: “Cata-104”)are placed in a Schlenk tube. The mixture is maintained at ambienttemperature for 20 h. The reaction is monitored by GPC. Polymerizationdoes not occur. The mixture is subsequently maintained at 70° C. for 15h. Polymerization does not occur. The mixture is then maintained at 160°C. for 1 h. A polymer with an M_(w) of 31 500 and with a polydispersityof 1.72 was obtained with an overall yield of 85%.

Example 2 Superbase Catalyst Formed by thebis(triphenylphosphoranylidene)methane/Alcohols Mixture:[Ph₃P═C═PPh₃/ROH]

Experimental Part

All the experiments were carried out under an inert atmosphere (dryargon). The toluene is dried over sodium and the CH₂Cl₂ over P₂O₅. The¹H, ³¹P and ¹³C NMR spectra were recorded on Bruker AC200 and WM250spectrometers. The chemical shifts are listed in ppm with respect toMe₄Si for ¹H and ¹³C NMR and with respect to H₃PO₄ for ³¹P NMR. Thecoupling constants are given in Hz. The purity of D₄ and M₂ wasconfirmed by GC (gas chromatography) (column 5% phenyl, 95% dimethylpolysiloxane, 25 m×0.32 mm, 0.5 μm, starting temperature 80° C., finaltemperature 250° C., δT 10° C./min; flame ionization detector). Thepolymerization reaction was monitored by GPC (gel permeationchromatography) (Waters 746 chromatograph, series of 3 columns (7.8×300mm): 2× styragel HR 5E and 1× styragel HR1, detector: refractometer,temperature: 35° C.). The molecular mass was estimated by externalcalibration from samples supplied by Rhodia (4 samples introduced 4times each). A linear correlation was obtained, R²=0.9984.

The tris(dimethylamino)phosphine (HMPT), the triphenylphosphine and thecarbon tetrachloride were purchased from Aldrich. D₄ and M₂ are suppliedby Rhodia. The triphenylphosphine was recrystallized from CHCl₃/CH₃OH(4/1). The tris(dimethylamino)phosphine was distilled under vacuum. CCl₄was purified and degassed on an Al₂O₃ column under argon. D₄ was driedover MgSO₄ for 24 h, dried by distillation with benzene and stored over4 Å molecular sieve. M₂ was distilled over CaH₂ under argon. Themethanol and the tert-butyl alcohol are dried over sodium and distilledunder argon. All these compounds are stored under argon.

[Chloro(triphenylphosphoranylidene)methyl]-triphenylphosphonium chloride(4)

This synthesis is carried out under the inspiration of the followingbibliographic reference: Appel, R.; Knoll, F.; Michel, W.; Morbach, W.,Wihler, H. -D.; Veltmann, H., Chem. Ber., 1976, 109, 58-70

7.6 g of triphenylphosphine are placed in a two-necked round-bottomedflask purged with argon. 15 ml of CH₂Cl₂ and 3.1 g of CCl₄ are addedusing a syringe. The reaction mixture is kept stirred at ambienttemperature for 20 h. 1.16 g of propylene oxide are subsequently addedusing a syringe. The reaction mixture is kept stirred at ambienttemperature for 1 h. Ether is added until a white precipitate is formed(approximately 25 ml) and then the solvent is withdrawn with a filteringhollow tube. The precipitate is washed with 8 ml of ether and driedunder vacuum at 80° C. for 6 h. The product is obtained in the form of awhite solid (w=4.7 g, 77%).

¹H NMR (CDCl₃): δ 5.28 (s, 1.5 H, CH₂Cl₂), 7.49 (m, 30 H). ¹³C NMR(CDCl₃): δ 123.4 (dd, J_(PC)=37.5 and 60.0 Hz, C_(i)), 129.7 (t,J_(PC)=5.0 Hz, C_(o,m)), 133.8 (t, J_(PC)=3.6 Hz, C_(o,m)), 134.02 (s,C_(p)), C-Cl is not observed. ³¹P NMR (CH₂Cl₂) 25.8.

Bis(triphenylphosphoranylidene)methane (5)

2 g of salt (4) are placed in a two-necked round-bottomed flask equippedwith a sintered glass and purged with argon. 8 ml of toluene and 0.6 mlof P(NMe₂)₃ are added using a syringe. The reaction mixture is keptstirred at 60° C. for 20 h. After having rapidly brought the temperatureto 100° C. (preheated oil bath), the mixture is filtered under argon. Ayellow solution is obtained and, after evaporation of the solvent undervacuum, the product (5) is obtained in the form of a yellow solid(w=0.97 g, 55%).

¹H NMR (C₆D₆): δ 7.81 (m, 12H), 7.02 (m, 18H). ³¹P NMR (C₇H₈): δ −4.5.

Polymerization of D₄ in the presence of the mixture: (5)/alcohols

-Method A. A solution of compound (5) in toluene is placed in a Schlenktube using a hollow tube. The solvent is evaporated under vacuum and theresidue is weighed. The alcohol is added to this residue. After stirringfor 5 min, D₄ and M₂ are added. The mixture is maintained at ambienttemperature. The reaction is monitored by GPC. The amounts of reactantand the results of the experiments are presented in table 4.

-Method B. A solution of compound (4) in toluene is placed in a Schlenktube using a hollow tube. The solvent is evaporated under vacuum and theresidue is weighed. The compound (5) is again dissolved in toluene (1ml), and 5 equiv. of alcohol are added to this solution. After stirringfor 5 min, D₄ and M₂ are added. The mixture is maintained at ambienttemperature and the reaction is monitored by GPC. The amounts ofreactant and the results of the experiments are presented in table 4.TABLE 4 Polymerization of D₄ in the presence of the mixture: compound(2)/alcohol Exp. Ylide ROH Time No. (ppm) eq./(2) Method (d) M_(w) %polym. 1 5000 50 (MeOH) A 2 <10 2 5000  5 (t-BuOH) A 1 <50000 40 2 60 35000  5 (t-BuOH) B 0.45 <50000 71 4 2000  5 (t-BuOH) B <5 39500 83

Example 3 Superbase Catalyst Formed by Reaction ofbis(iisopropylmethylphosphonium)methylene diiodide with potassiumtert-butoxide

1) Snthesis of tris(dimethylamino)isopropylphosphonium idodide:

18.7 g (110 mmol) of 2-iodopropane are added to 40 ml of diethoxymethanecomprising 5 ml (27 mmol) of HMPT in a two-necked flask equipped with areflux condenser. The mixture is left at reflux for 5 days. Thephosphonium salt precipitates in the form of a white powder. Theprecipitate is filtered off and washed with diethoxymethane (2×5 ml).The product is dried under reduced pressure at ambient temperature for10 hours. The yield is 65% (purity: 98%). The compound can be purifiedby recrystallization from acetonitrile. The ¹H NMR (CD₃CN), ¹³C{¹H} NMR(CD₃CN) and ³¹P{¹H} NMR (CH₂Cl₂) data are in agreement with thestructure of the expected product.2) Polymerization Test/

0.020 g (0.21 mmol) of potassium tert-butoxide and 0.077 g (1.04 mmol)of dry tert-butanol are introduced into a Schlenk tube. The combinedmixture is dissolved in 5 ml of dry THF and added dropwise, using ahollow tube, to a suspension of 0.023 g (0.069 mmol) oftris(dimethylamino)isopropyl-phosphonium iodide in 2 ml of dry THF. Themixture is stirred at ambient temperature for 15 minutes. 10.23 g (34.5mmol) of D₄ and 0.140 g (0.863 mmol, 25 000 ppm) of M₂ are then added tothe solution; the amount of initiator being set at 2000 ppm. The mixtureis maintained at ambient temperature and the progress of thepolymerization is monitored by GPC. After 24 hours, the degree ofconversion is estimated at 70% (M_(n)=8418; PI=1.47).

Example 4 Superbase Catalyst Formed by Reaction ofbis(diisopropylmethylphosphonium)methylene diiodide with potassiumtert-butoxide

1) Synthesis of bis(dichlorophosphino)methylene:

32 g (1.186 mol) of aluminum filings are suspended in 300 ml (5.5 mol)of distilled dichloromethane in a two-necked flask equipped with areflux condenser. 10 ml (0.116 mol) of dibromoethane are then addeddropwise and the reaction mixture is heated at 45° C. for 48 hours.After returning to ambient temperature, the gray salt formed is filteredand the orange-colored solution is transferred via a hollow tube into adropping funnel surmounting a three-necked flask also equipped with areflux condenser and comprising 107 ml (1.226 mol) of PCl₃ and 100 ml ofdistilled dichloromethane. The solution is added dropwise until gentlereflux is obtained and then the mixture is heated at 45° C. for 3 hours.After returning to ambient temperature, the dropwise addition issubsequently carried out over 108 ml (1.158 mol) of POCl₃ and 94.5 g(1.267 mol) of KCl. The mixture is brought to 45° C. for an additional 3hours. After filtering off the salts and evaporating the solvents underreduced pressure, the expected product is purified by distillation(B.p.=43° C./0.5 mmHg) and exists in the form of a beige oil. Weightobtained: 12.17 g. Yield: 10%. The ¹H NMR (CDCl₃) and ³¹P{¹H} NMR(CDCl₃) data are in agreement with the structure of the expectedproduct.2) Synthesis of bis(diisopropylphosphino)methylene:

3.058 g (114.68 mmol) of magnesium turnings are placed in 10 ml of dryethyl ether in a three-necked flask equipped with a reflux condenser anda dropping funnel. 15.51 g (114.68 mmol) of 2-bromo-propane aredissolved in 40 ml of dry ethyl ether in the dropping funnel and thesolution is added dropwise at ambient temperature. The round-bottomedflask is subsequently cooled in ice and 5.5 g (22.94 mmol) ofbis(dichlorophosphino)methylene in solution in 30 ml of dry ethyl ether,are added dropwise. After evaporating the ether under reduced pressure,three extractions with pentane are carried out (3×50 ml). Thediphosphine is purified by tube-to-tube distillation and exists in theform of a colorless oil. Weight obtained: 2.61 g. Yield: 45%. The ¹H NMR(CDCl₃) and ³¹P {¹H} NMR (CDCl₃) data are in agreement with thestructure of the expected product.3) Synthesis of bis(diisopropylmethylphosphonium)-methylene diiodide:

1.06 g (4.27 mmol) of bis(diisopropyl-phosphino)methylene are dissolvedin 20 ml of dry THF in a Schlenk tube. 1.35 g (9.40 mmol) of methyliodide are added thereto dropwise and the mixture is brought to 40° C.for 48 hours. After returning to ambient temperature, the diphosphoniumis filtered off, washed with 2×5 ml of dry THF and isolated in the formof a white powder. Weight obtained: 1.96 g. Yield: 85%. The ¹H NMR(DMSO), ¹³C{¹H} NMR (DMSO) and ³¹P {¹H} NMR (DMSO) data are in,agreementwith the structure of the expected product.4) Synthesis of the Phosphonium Tert-Butoxides:

0.085 g (0.891 mmol) of potssium tert-butoxide and 0.33 g (4.45 mmol) ofdry tert-butanol are introduced into a Schlenk tube. The combinedmixture is dissolved in 8 ml of dry THF and is added dropwise, via ahollow tube, to a suspension of 0.158 g (0.297 mmol) ofbis(diisopropylmethylphosphonium)methylene diiodide in 2 ml of dry THF.The mixture is stirred at ambient temperature for 15 minutes. PhosphorusNMR is quantitative and the initiator is used as is without additionalpurification. ³¹P{¹H} NMR (C₆D₆) δ=36.2 ppm.

5) Polymerization of D₄:

0.038 g (0.39 mmol) of potassium tert-butoxide and 0.147 g (2.0 mmol) ofdry tert-butanol are introduced into a Schlenk tube. The combinedmixture is dissolved in 8 ml of dry THF and is added dropwise, via ahollow tube, to a suspension of 0.070 g (0.133 mmol) ofbis(diisopropylmethylphosphonium)methylene diiodide in 2 ml of dry THF.The mixture is stirred at ambient temperature for 15 minutes. 7.89 g(26.6 mmol) of D₄ and 0.107 g (0.665 mmol, 25 000 ppm) of M₂ are thenadded to the solution; the amount of initiator being set at 5000 ppm.The mixture is maintained at ambient temperature and the progress of thepolymerization is monitored by GPC. After 1 hour, the degree ofconversion is estimated at 40%, it is 55% after 3 hours and 80% after 24hours (M_(w)=7726; PI=1.53).

1-23. (canceled)
 24. A process for the preparation ofpolyorganosiloxanes (POSs) comprising the steps of: a) carrying out apolycondensation/redistribution reaction of oligosiloxanes in thepresence of a catalyst in a reaction medium comprising at least onestrong base selected from the group consisting of: aminophosphoniumylide derivatives of following formula (I):

wherein: the R¹ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;the R² symbols, which are identical to or different from one another,each represent a hydrogen, an alkyl, an aryl, an aralkyl or analkylaryl; and R corresponds to hydrogen or to an alkyl, an aryl, anaralkyl or an alkylaryl; and phosphoranylidene derivatives of followingformulae (II), (II^(x)), (II′) and (II^(x′)):

wherein: the R⁴ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;the R⁵ symbols, which are identical to or different from one another,each represent a radical corresponding to the same definition as thatgiven above for R⁴; R′ corresponds to hydrogen or an alkyl, an aryl, anaralkyl or an alkylaryl; and x, y, z, m¹, m², x′, y′ and z′ are positiveintegers with x=y×z, m¹×m²=2, and x′=2×y′×z′; and b) recovering saidpolyorganosiloxanes prepared in step a).
 25. The process as claimed inclaim 24, wherein the OR⁻ or OR′⁻ anion is nucleophilic and has a pK_(a)of between 10 and
 30. 26. The process as claimed in claim 24, whereinthe R or R′ radical is hydrogen or C₁-C₆ alkyl.
 27. The process asclaimed in claim 24, wherein the polycondensation/redistribution iscarried out at a temperature T (° C.) such that T≦100.
 28. The processas claimed in claim 27, wherein the temperature T (° C.) is such that15≦T≦70.
 29. The process as claimed in claim 24, wherein the catalyst Cis present in the reaction medium in a concentration ≦10 000, expressedin ppm with respect to the starting oligosiloxanes.
 30. The process asclaimed in claim 24, wherein the polycondensation/redistribution ishalted by heating the reaction medium, or by addition of water to thereaction medium.
 31. The process as claimed in claim 24, wherein thecatalyst is of formula (I) and in that, on the one hand, the R¹ radicalis a C₁-C₆ alkyl, and, on the other hand, the R² radical is a R¹ radicalor hydrogen.
 32. The process as claimed in claim 24, wherein thecatalyst is of formula (I) and at least one solution of at least oneprecursor (Ip1):

wherein the R¹ and R² radicals correspond to the same definition as thatgiven above, R² being different from hydrogen, in at least one solventof formula ROH, with R as defined above, is added to the reaction mediumin step a).
 33. The process as claimed in claim 32, wherein the solventROH is in excess with respect to the compound(s) (Ip1).
 34. The processas claimed in claim 32, wherein the solution of (I) in ROH comprises atleast one other solvent of (Ip1).
 35. The process as claimed in claim24, wherein the catalyst is of formula (II) or (II^(x)) and at least onesolution of at least one precursor (IIp1):

wherein the R⁴ radicals correspond to the same definition as that givenabove, in at least one solvent of formula R′OH, with R′ as definedabove, is added to the reacton mixture in step a).
 36. The process asclaimed in claim 35, wherein the solvent R′OH is in excess with respectto the compound(s) (IIp1).
 37. The process as claimed in claim 35,wherein the solution of (IIp1) in R′OH further comprises at least oneother solvent S* of(Ip1).
 38. The process as claimed in claim 37,wherein a solution of (IIp1) in S* is prepared and this solution ismixed with the solvent(s) R′OH, the compound(s) (IIp1) used to preparethis solution in S* being composed of one (or more) evaporationresidue(s).
 39. The process as claimed in claim 24, wherein the startingoligosiloxanes correspond to the following general formula:

wherein R^(a) represents hydrogen or an alkyl or aryl radical and R^(b)corresponds to an alkyl or an aryl, optionally comprising one or moreheteroatoms and optionally substituted by halogens, and p≧2.
 40. Theprocess as claimed in claim 24, wherein the starting oligosiloxanes arecyclic and correspond to the following general formula:

wherein R^(c) represents hydrogen or an alkyl or aryl radical, and3≦q≦12.
 41. A catalyst for the preparation of Polyorganosiloxanes (POSs)by polycondensation/redistribution of oligosiloxanes, comprising atleast one strong base of following formula (I):

wherein: the R′ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;the R² symbols, which are identical to or different from one another,each represent a hydrogen, an alkyl, an aryl, an aralkyl or analkylaryl; and R corresponds to hydrogen or to an alkyl, an aryl, anaralkyl or an alkylaryl.
 42. A catalyst for the preparation ofpolyorganosiloxanes (POSs) by polycondensation/redistribution ofoligosiloxanes, of a compound comprising at least one strong baseselected from the group consisting of phosphoranylidene derivatives offollowing formulae (II), (II^(x)), (II′) and (II^(x′)):

wherein: the R⁴ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;the R⁵ symbols, which are identical to or different from one another,each represent a radical corresponding to the same definition as thatgiven above for R⁴; R′ corresponds to hydrogen or an alkyl, an aryl, anaralkyl or an alkylaryl; and x, y, z, m¹, m², x′, y′ and z′ are positiveintegers with x=y×z, m¹×m²=2, and x′=2×y′×z′.
 43. A derivative of theaminophosphonium ylide derivatives of following formula (I):

wherein: the R¹ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;the R² symbols, which are identical to or different from one another,each represent a hydrogen, an alkyl, an aryl, an aralkyl or analkylaryl; and R corresponds to hydrogen or to an alkyl, an aryl, anaralkyl or an alkylaryl.
 44. A phosphoranylidene derivative of followingformulae (II), (II^(x)), (II′) or (II^(x′)):

wherein: the R⁴ symbols, which are identical or different, eachrepresent an alkyl, an aryl, an aralkyl or an alkylaryl; the R⁵ symbols,which are identical or different, each represent a radical correspondingto the same definition as that given above for R⁴; R′ corresponds tohydrogen or an alkyl, an aryl, an aralkyl or an alkylaryl; and x, y, z,m¹, m², x′, y′ and z′ are positive integers with x=y×z, m¹×m²=2, andx′=2×y′×z′.
 45. A catalyst precursor in the preparation ofpolyorganosiloxanes (POSs) by polycondensation/redistribution ofoligosiloxanes, of following formulae (IIp1) or (IIp2):

wherein: the R⁴ symbols, which are identical to or different from oneanother, each represent an alkyl, an aryl, an aralkyl or an alkylaryl;and X corresponds to a chlorine, bromine or iodine atom.